Thanks adoby. I think it might be a combination of ALIEN enemies and ghosts in the machines.
I was definitely trying to connect to the right IP address and there's nothing wrong with the cable (it was connecting to the previous incarnation of the same box without issues) but direct connection with a monitor revealed that it was not booting, with a string of errors.... Nothing was loose.
The installation was fine when it was in another room....
Unfortunately, yet another "drama" had me reach the end of my tether and I've given up.